ChemistryA LevelEquilibria

Partial pressure formula

The partial pressure formula as it is used in A Level Chemistry, taken from the A Level Chemistry formula sheet.

The formula

p_A = x_A \times p_{\text{total}}

x = mole fraction

Write the formula down before substituting — most mark schemes award a method mark for a correct, clearly quoted formula.
Check every quantity is in consistent units before you substitute, then substitute in one step so the working stays easy to follow.
Show the rearrangement rather than jumping to the answer, and give the final value to the accuracy the question asks for.

K_c = \dfrac{[\text{C}]^c[\text{D}]^d}{[\text{A}]^a[\text{B}]^b}

K_p = \dfrac{p_C^{\,c}\,p_D^{\,d}}{p_A^{\,a}\,p_B^{\,b}}

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